Echelon grating for reflecting ultra short waves



y 1933- l R. H. DARBORD 46 ECHELON GRATING FOR REFLECTING ULTRA SHORTWAVES Filed July 10, 1931 INVENTOR RENE H. DARBORD ATTOR EY RENE H.DARBORD, OF PARIS, FRANCE, ASSIGNOR TO INTERNATIONAL COMMUNICA PatentedMay 2, 1933 UNITED, STATES PATENT? OFFICE TIONS LABORATORIES, INC., OF.NEW YORK, N. Y., A CORPORATION OF NEW YORK ECHELON GRATING FORREFLEGTING ULTRA SHORT WAVES App-lication filed July 10,

' This invention relates generally to ultrashort wave systems and moreparticularly to reflecting systems for eificiently utilizing theradiations from a high frequency source for purposes of transmission andreception.

The object of the present invention is to retain the advantages ofdiflracting systems of the zone plate type, which permit the ultrashortwaves to be diffracted so as to be, to a certain degree, in phase at adistant point, and,'at the same time, to provide a diffracting systemthatwill concentrate a greater portion of the diffracted energy in abeam proceeding in the desired direction. r

Heretofore, directional systems for ultrashort waves have beenconstructed by utilizing the well known optical principles applicable tozone plates. These systems have been found, however, to'be somewhatineiflcient because of the wide discrepancy between the ldirection ofmaximum intensity of the diffracted rays and the desired direction oftransmission. Tobe explicit, the direction of maximum intensity of thediffracted-rays is inclined, while the desired direction'of transmissionof these rays is parallel to the axis of the system. This discrepancy isthe more accentuated as the incidence of the rays upon the zone plate"becomes more oblique. l v

These disadvantageous effects are eliminated by the use of echelonreflectors, which not onlylj'cause -the"difl'racted rays to arrive inphase at the receiving point, but also diffract the rays in a directionparallel to the axis of the system, and thus eflect a concentration ofthe rays in the desired direction of transmission. Thislast-mentionedresult is, in itself, a noteworthy improvement over zone platereflectors.

These echelon reflectors comprise circular rings, parabolic incross-section, each of the rings having the same focus and all the ringsbeing successively placed'at focal differences differing by one-half awave-length or by multiples of one-half a wavelength. Be;- cause of thedifference in the focal distances of the several rings, the wavesreflected from them are'reflected in phase; while, in accordance withgeometrical optics, the waves are 1931. Serial No. 549,926."

also diffracted in a direction parallel to the common axis of the rin swith a resulting concentration of the di racted energy in: a beamproceeding in the desired direction.

A preferred embodiment of the invention a Referring now to Fig. 1, thereis shown at A an echelon parabolic reflector, andatB an element whichmay be either. a transmits ting or receiving antenna, althoughthe'description willbe limited to the case'where B is a transmittingantenna, The element B is placed at the'focus of the echelon reflector Aand at the center of a spherical mirror C. A suitable source or suitablereceiver; of high frequency oscillations, depending upon Whether B is atransmitting or receiving antenna, is connected to the element B throughthe spherical mirror C. The echelon refflector A is constructed of anumber of rings, such as 1, 2, 3 and 4, which are parabolic incross-section, as is shown in Fig. 1, and circular in aperture, as isshown in Fig. 2.

Each of these rings may be provided with any kind of metallic surfacethat'is capable of reflecting the ultra-short Waves. This surface, as iswell known in the art, may be very thin and may be composed of a numberof diflerent metals. One method of construction is to attach theparabolic metal rings to supports, one of which is illustrated in Fig.

3, and to fasten these supports radially on a properly insulatedvertical frame, such as 5, shown in Fig. 2. In this way the parabolicrings are firmly held in place.

' Theparabolic rings 1, 2, 3 and i, as previously mentioned, have focaldistances that difl'er by half a wave-length. For example, ring 1 has afocal distance one-half a wavelength greater than the focal distance ofring 2,'and the same relation holds true for rings 2 and 3, and rings 3and 4. vThe length of each parabolic portion is limited by aconsideration that will now be explained. In order that the waves fromthe high frequency surface 13 shall be reflected in phase from theparabolic rings comprising the echelon reflector A, it is essential thatthe distances traversed by the waves, when reflected from the severalrings, differ by integral wavelengths or by multiples of wave-lengths.Considering for the moment the path of Waves reflected from parabolicrings 1 and 2,

it is evident that waves reflected from ring 1 traverse a distance 10-9plus 9-8 greater than the distance traversed by the waves reflected fromthe parabolic ring 2. But the distance 10-9 is equal to one-half awave-length since rings 2 and 3 have focal distances differing by thatamount. In order, therefore, that the Waves reflected from rings 1 maybe in phase with the waves reflected from ring 2, the distance 9-8 mustbe equal to half a wave-length. This is an essential condition of thestructure. When this condition has been fulfilled, however, it isevident that the waves reflected from the severalparabolic ringscomprising the echelon reflector A are in phase.

It is to be understood that the echelon parabolic reflector may have anynumber of parabolic rings. However, to avoid undue cumbersomeness of thereflector, the number of rings is ordinarily limited to four or five.Furthermore, it is unnecessary that the parabolic rings 1, 2, 3, etc.have a cross-section in the exact form of a parabolic arc; for it issufficiently exact to make the rings conical in cross-section. Thecenter ring 4, although having a larger surface than the other rings,may also be made conical in cross-section. This is possible because thespherical mirror C limits the effectiveness of the ring 4 by stoppingthe rays transmitted from the center of the ring. When the rings areconical in cross-section the echelon reflector is more easilyconstructed than it is when the rings are parabolic in cross-section.This is evident from the-fact that the cone is a developable surface andit is, therefore, unnecessary, as in the case of a parabolic ring, tohave a form upon which the metal rings are mounted. In this case thedifferent rings are approximately in the same plane and can be readilymounted on an insulated support by means of wooden triangles.

The source of high frequency oscillations B may be a doublet or any ofthe other suitable sources well known in the art. The spherical mirror Cis placed about the high frequency source B with its aperture facing theechelon reflector A for the purpose of re fleeting back upon the echelonzone plate the waves from the source B whose initial direction was awayfrom the zone plate. As the use of a mirror for the purpose mentioned iswell known in the art, no further description is thought necessary here.

It is evident that radiations from the source of high frequencyoscillations B will be projected upon the echelon reflector A with theaid of the spherical mirror C and that these radiations will bereflected in base from rings 1 to 4 and will also be re ected alonglines 13 and 14 in a direction parallel to the axis 6 of the echelonreflector A.

In Fig. 2 is shown in front elevation a detailed view of echelonreflector A. This reflector is provided with five instead of four rings.It has been previously mentioned, however, that the number of rings usedmay vary. Each of the rings is shown mounted on a support such as isshown in detail in Fig. 3 and these supports are, in turn, fastenedradially to an insulated frame 5 which is mounted on standards 6 and 7.

Although the system has been described particularly with reference to atransmitting system, it is, of course, to be understood that the echelonreflector may also be used as a receiver.

The above description has been given to exemplify a preferred embodimentof the invention and it is to be understood that the invention is not tobe unnecessarily limited by the particular embodiment herein described,but is to be as broad as the appended claims.

What is claimed is: i

1. In ultra-short wave systems, the combination of a source of suitableoscillations, and a reflecting device comprising a plurality ofconcentric rings, cross-sections of said rings being parts of confocalparabolas, the focal distances of the parabolas differing by onehalf awave-length or by a multiple of half a wave-length.

2. As a new article of manufacture, a reflecting device comprising aplurality of 0011- centric rings, said rings being parabolic incross-section, being placed at focal distances differing by one-half awavelength or multiples of half a wave-length, and each having a surfaceadapted to reflect ultrashort waves. i i

3. In an ultra-short Wave system, the combination of a source ofsuitable oscillations, a reflecting device comprising a plurality ofconcentric rings, the surfaces of said rings being substantiallyparaboloidal and being suitably spaced from one another and from saidsource, whereby the oscillations fromsaid source are reflected by saiddevice sub stantially in phase and in a direction parallel to the commonaxis of said rings.

4:. In an ultra-short wave system, the combination of a reflectingdevice comprising a plurality of concentric rings, a source of suit ableoscillations located at the common focus of said rings, the surfaces ofsaid rings be ing substantially paraboloidal, whereby the oscillationsfrom said source are reflected by said devices substantially in phase.

RENE H. DARBORD.

